Textile designers are very creative. This is necessary because of seasonal factors and because the public taste continually changes, so the industry continually demands new products. Many designers in this industry would like the ability to custom-make their own yarns, so their products would be more unique, and so as to provide more flexibility in designing textiles.
For textile purposes, a "textile" yarn must have certain properties, such as sufficiently high modulus and yield point, and sufficiently low shrinkage, which distinguish these yarns from conventional feed yarns that require further processing before they have the minimum properties for processing into textiles and subsequent use. Generally, hereinafter, we refer to untextured filament yarns as "flat" yarns and undrawn "flat" filament yarns as "feed" or as "draw-feed" filament yarns. Filament yarns which can be used as a "textile" yarn without need for further drawing and/or heat treatment are referred to herein as "direct-use" filament yarns. It will be recognized that, where appropriate, the technology may apply also to polyester filaments in other forms, such as tows, which may then be converted into staple fiber, and used as such in accordance with the balance of properties that is desirable and may be achieved as taught hereinafter.
It is important to recognize that what is important for any particular end-use is the combination of all the properties of the specific yarn (or filament), sometimes in the yarn itself during processing, but also in the eventual fabric or garment of which it is a component. It is easy, for instance, to reduce shrinkage by a processing treatment, but this modification is generally accompanied by other changes, so it is the combination or balance of properties of any filament (or staple fiber) that is important. It is also understood that the filaments may be supplied and/or processed according to the invention in the form of a yarn or as a bundle of filaments that does not necessarily have the coherency of a true "yarn", but for convenience herein a plurality of filaments may often be referred to as a "yarn" or "bundle", without intending specific limitation. Many yarns have had several desirable properties and have been available in large quantities at reasonable cost; but, hitherto, there has been an important limiting factor in the usefulness of most polyester flat yarns to textile designers, because only a limited range of yarns has been available from fiber producers, and the ability of any designer to custom-make his own particular polyester flat yarns has been severely limited in practice. The fiber producer has generally supplied only a rather limited range of polyester yarns because it would be more costly to make a more varied range, e.g. of deniers per filament (dpf), and to stock an inventory of such different yarns.
Conventional flat polyester filament yarns have typically been prepared, for example, by melt-spinning at low or moderate speeds (to make undrawn yarn that is sometimes referred to as LOY and MOY) and then single-end drawing and heating to reduce shrinkage and to increase modulus and yield point. Conventional polyester filaments have combinations of properties that, for certain end-uses, could desirably be improved, as will be indicated hereinafter. Recently, there has been interest in using flat undrawn filament yarns (e.g., LOY, MOY, and most especially POY), which have generally been cheaper than drawn yarns, and incorporating a drawing step in the beaming operation, as disclosed, e.g., by Seaborn, U.S. Pat. No. 4,407,767. This process is referred to herein as "warp-drawing", but is sometimes called draw-beaming or draw-warping.
As disclosed, e.g., in the parent application (U.S. Pat. No. 5,055,447 referred to hereinabove, the disclosure of which is hereby incorporated herein by reference), it was known that conventional polyester undrawn LOY, MOY, and POY (defined hereinafter) draw by a necking operation; i.e., such conventional undrawn polyester filaments have a natural draw-ratio (NDR) and that drawing such polyester filaments at draw ratios less than this natural draw-ratio (herein referred to as partial-drawing, i.e., drawing to a residual elongation of more than about 30% in the drawn yarns) produces irregular "thick-thin" filaments which are considered inferior for most practical commercial purposes (unless a specialty yarn is required, to give a novelty effect, or special effect). For filament yarns, the need for uniformity is particularly important, more so than for staple fiber. Fabrics from flat yarns show even minor differences in uniformity from partial drawing of conventional undrawn polyester yarns as defects, especially when dyeing these fabrics. Thus, uniformity in flat filament yarns is extremely important.
Undrawn polyester filaments were unique in this respect because nylon filaments and polypropylene filaments did not have this defect. Thus, it has been possible to take several samples of a nylon undrawn yarn, all of which have the same denier per filament, and draw them, using different draw ratios, to obtain correspondingly different deniers in the drawn yarns, as desired, without some being irregular thick-thin filament yarns, like partially drawn polyester filament yarns. POY stands for partially oriented yarn POY, meaning spin-oriented yarn spun at speeds of, e.g., 2.5-3.5 km/min for use as draw feed yarns for draw-texturing as suggested in Petrilie, U.S. Pat. No. 3,771,307 and Piazza & Reese, U.S. Pat. No. 3,772,872. These draw-texturing feed yarns (DTFY) had not been used, e.g., as textile yarns, because of their high shrinkage and low yield point, which is often measurable as a low T.sub.7 (tenacity at 7% elongation) or a low modulus (M). In other words, POY used as DTFY are not textile yarns (sometimes referred to as "hard yarns") that can be used as such in textile processes, but are draw feed yarns (DFY) that are drawn and heated to increase their yield point and reduce their shrinkage so as to make textile yarns. MOY means medium oriented yarns, and are prepared by spinning at somewhat lower speeds than POY, e.g., 1.5-2.5 km/min, and are even less "hard", i.e., they are even less suitable for use as textile yarns without drawing. LOY means low oriented yarns, and are prepared at much lower spinning speeds of the order of 1.5 km/min or much less.
When conventional polyester undrawn POY of high shrinkage are prepared at higher spinning speeds, there is still generally a natural draw-ratio (NDR) at which these yarns prefer to be drawn, i.e., below which the resulting yarns are irregular; although the resulting irregularity becomes less noticeable, e.g., to the naked eye or by photography, as the spinning speed of the precursor feed yarns is increased, the along-end denier variations of the partial drawn yarns are nevertheless greater than are commercially desirable, especially as it is generally desired to dye the resulting fabrics or yarns. Denier variations often mean the filaments have not been uniformly oriented along-end, and variations in orientation affect dye-uniformity. Dyeing uniformity is very sensitive to variations resulting from partial drawing, as reported, for instance, by Bosley, et al. U.S. Pat. No. 4,026,098; Lipscomb, et al. U.S. Pat. No. 4,147,749; Nakagawa, et al. U.S. Pat. No. 4,084,622; Allen, et al. U.S. Pat. No. 3,363,295. It has also been reported that such prior art drawing results in along-end spontaneous crimp on shrinkage (Schippers U.S. Pat. No. 4,019,311; col. 10/lines 44-59 and col. 11/lines 24-31). Both of these are undesirable defects for end-uses requiring uniform along-end dyeability. This has severely limited the utility of conventional spin-oriented polyester POY filament yarns, for example, as a practical draw-warping feed yarn.
Thus, previously, even with POY, such as has been used as feed yarn for draw-texturing, it had not been practical to draw-warp the same such POY to two different dpfs that vary from each other by as much as 10% and obtain two satisfactory uniform drawn yarns. Thus, it will be understood that a serious commercial practical defect of prior suggestions for draw-warping most prior undrawn polyester (POY, MOY or LOY) had been the lack of flexibility in that it had not been possible to obtain satisfactory uniform products using draw ratios below the natural draw-ratio for the polyester feed yarn.
So far as is known, it had not previously been suggested, except in the parent application, that a draw process (such as a draw-warping process) be applied to a polyester textile yarn, i.e., one that was itself already a direct-use yarn, such as having shrinkage and tensile properties that made it suitable for direct use in textile processes such as weaving and knitting without first drawing. Indeed, to many skilled practitioners, it might have seemed a contradiction in terms to subject such a yarn to draw-warping, for example, because such a yarn was already a textile yarn, not a feed yarn that needed a drawing operation to impart properties useful in textile processes such as weaving or knitting.
According to the parent application, processes were provided for improving the properties of feed yarns of undrawn polyester filaments (especially undrawn polyester filament feed yarns having the shrinkage behavior of the spin-oriented polyester filaments disclosed by Knox in U.S. Pat. No. 4,156,071, and by Frankfort & Knox in U.S. Pat. Nos. 4,134,882 and 4,195,051). Such processes involved drawing with or without heat during the drawing and with or without post heat-treatment, and are most conveniently adapted for operation using a draw-warping machine, some such being sometimes referred to as draw-beaming or warp-drawing operations; but such benefits may be extended to other drawing operations, such as split and coupled single-end drawing (or of small number of ends, typically corresponding to the number of spin packages per winder or spin position of a small unit of winders) and to various draw (and no-draw) texturing processes for providing bulky filament yarns.